Polyaluminum chloride (PAC) is the name given to the family of compounds defined by the formula:Alm(OH)nCl3m−n 
Where 0<n≦3m and where m≧1. The degree of neutralization (i.e., the OH to Al ratio) is known as the basicity. In the case of polyaluminum chlorides the basicity is defined by the formula n/3 m. The highest basicity PAC of commercial interest is the polyaluminum chloride with 83% basicity known as aluminum chlorohydrate (ACH); it has an empirical formula of Al2(OH)5Cl.
High basicity, high purity PAC, including ACH, is commonly used either alone or in combination with zirconium hydroxyl-halides to produce antiperspirants. Polyaluminum chloride, including ACH used for this purpose is prepared by the reaction of hydrochloric acid or aluminum chloride or low-basicity PAC with aluminum metal. Thus, U.S. Pat. No. 6,245,325 states that the reaction of hydrochloric acid with aluminum metal is generally known and is the method generally utilized to prepare high basicity PAC and ACH solutions on a commercial basis. U.S. Pat. No. 6,902,724 and references contained therein teach the reaction of aluminum chloride with aluminum metal to produce aluminum antiperspirant salt compositions. U.S. Pat. No. 2,854,382, U.S. Pat. No. 4,331,609, U.S. Pat. No. 4,775,528, U.S. Pat. No. 5,955,064, U.S. Pat. No. 6,126,928 and U.S. Pat. No. 6,902,724 teach the preparation of aluminum-zirconium antiperspirant salt compositions whereby zirconium-hydroxyl chlorides are combined with high basicity PAC and or ACH that is prepared from aluminum metal as discussed above.
Aluminum metal is an expensive source of aluminum ion when compared to other sources of aluminum ion like aluminum trihydrate. Based on historical pricing relationships, aluminum from aluminum metal costs about three times as much as aluminum from aluminum trihydrate.
Aluminum and aluminum-zirconium antiperspirants have been known for several decades (see U.S. Pat. No. 2,854,382 (Grad), U.S. Pat. No. 4,331,609 (Orr) and U.S. Pat. No. 4,871,525 (Giovanniello) and references contained therein). These products typically contain an antiperspirant active in the form of an aluminum and/or zirconium salt; said salts are formed by partial neutralization of acidic aluminum (Al+3) and/or zirconium (Zr+4) metal ions.
The partial neutralization of these ions results in the formation of aluminum and zirconium hydrolysis products of complex structure. The performance (i.e., efficacy) of aluminum and aluminum-zirconium antiperspirant salt compositions is dependent on the molecular distribution of these hydrolysis products. In general, low molecular weight hydrolysis products favor better performance by providing increased sweat inhibition. Low molecular weight antiperspirant salt compositions which provide increased sweat inhibition are said to have enhanced efficacy.
Aluminum and aluminum-zirconium antiperspirants salts function by forming insoluble metal hydroxides in the ducts of sweat glands, this blockage prevents perspiration. Low molecular weight antiperspirant salts penetrate more deeply into these ducts than their high molecular weight counterparts. Thus, deeper penetration provides more effective blockage. (See Quatrale, et. al., The Mechanism of Antiperspirant Action of Aluminum Salts, Journal of the Society of Cosmetic Chemists, May-June 1981, 32:107-136 & Journal of the Society of Cosmetic Chemists, November-December 1985, 36:435-440).
High pressure liquid chromatography (HPLC) employing size exclusion columns is commonly used to characterize the molecular weight distribution and efficacy of aluminum and aluminum-zirconium antiperspirant salts. Size exclusion chromatographic columns have a high affinity for low molecular weight materials and a low affinity for high molecular weight materials. This difference in affinity causes high molecular weight materials to be eluted more quickly than low molecular weight materials. Accordingly, this HPLC technique separates and identifies the components of aluminum and aluminum-zirconium antiperspirant salts with respect to molecular weight. Five distinct species have been identified by this technique. The highest molecular weight species is eluted first and referred to as Peak 1 material. The lowest molecular weight species is eluted last and referred to as Peak 5 material. FIG. 2 shows a HPLC diagram of an aluminum antiperspirant salt. The relative area of each peak indicates the amount of the various components present. In this diagram Peaks 1 thru 3 have a greater relative area than Peaks 4 & 5, indicating that this sample is primarily composed of high molecular weight, low efficacy components. (In some references authors have used the term “band” instead of the term “peak” to describe the results of HPLC analysis. Generally, Bands I, II, III and IV of one system correspond to Peaks 1+2, (Band I), 3, 4, and 5 of the other system.)
Review of the literature shows that the low molecular weight species in Peak 4 and Peak 5 are responsible for increased sweat inhibition and that enhanced efficacy results when there is a preponderance of these peaks. These reports indicate there are at least two distinct groups of materials in which there is a preponderance of Peaks 4 and 5. These two groups of materials are referred to herein as Group 1 Materials and Group 2 Materials; both of which exhibit the attribute of enhanced efficacy. These two groups are differentiated with respect to their stability in water. As elaborated below, Group 1 Materials are unstable in water and decompose rapidly to high molecular weight low efficacy materials. Group 2 Materials are stable in water; this characteristic provides certain commercial benefits as explained below.
Group 1 Materials are characterized by their Peak 4 content in comparison to their Peak 3 content. A Peak 4 to Peak 3 area ratio of 0.5 or greater provides for increased sweat inhibition. These materials typically contain a preponderance of Peak 4 and a low level of Peak 3 and Peak 5. For example, 83% basic aluminum chlorohydrate (produced by the reaction of hydrochloric acid with aluminum metal) primarily contains high molecular weight species of Peaks 1 through 3. However ACH is converted to a Group 1 Material by heating a dilute solution (e.g. about a 10% salt concentration by weight) at about 80-100° C. for about 4 to 20 hours. (See U.S. Pat. No. 4,359,456 (Gosling), U.S. Pat. No. 4,775,528 (Callaghan), U.S. Pat. No. 5,955,064 (Giovanniello), U.S. Pat. No. 6,149,897 (Swaile) and references contained therein).
Table 1, Example 1 shows the composition of ACH with about 83% basicity prepared by the reaction of hydrochloric acid with aluminum metal. This material contains about 74% of high molecular weight species (Peaks 1 through 3) and about 26% low molecular weight species (Peak 4 and 5) and a Peak 4 to Peak 3 ratio of about 0.1. The HPLC of this material is shown in FIG. 1A. (For the sake of comparison, FIG. 2 is the HPLC taken from the literature of a non-enhanced aluminum antiperspirant salt of similar composition.)
Table 1 Example 2 shows the composition of the same material after heating a dilute (8% salt solution) at 100° C. for two hours. As expected, high molecular weight Peaks 1 through Peak 3 materials are diminished and low molecular weight Peak 4 materials are enhanced. In this example, the solution contains about 74% of the low molecular weight species in Peak 4, about 83% of Peak 4 & 5 and a Peak 4 to Peak 3 ratio of greater than 4.0. The HPLC of this material is shown in FIG. 1B. (For the sake of comparison, FIG. 3 is the HPLC taken from the literature of an aluminum-zirconium antiperspirant salt with Peak 4 to Peak 3 ratio of greater than about 1.3.)
In summary, Group 1 Materials are prepared through a multi-step process that requires manufacturing high basicity PAC from aluminum metal. Many of the references cited herein teach the use of aluminum powder which is more expensive than other sources of aluminum metal. The high basicity PAC prepared in the first step is then enhanced by diluting it to a 10% salt or less concentration and heating it for several hours at about 100° C. If an enhanced aluminum-zirconium antiperspirant salt is being prepared the zirconium component is added either before or after the heat treating process. The dilute solution of enhanced efficacy antiperspirant salt is then rapidly spray dried in order to obtain the enhanced efficacy antiperspirant salt. Said antiperspirant salt is then formulated into consumer products.
One undesirable attribute of Group 1 Materials is their lack of stability in aqueous solution. These materials must be rapidly dried in order to preserve the increased low molecular weight, Peak 4 content. In the absence of rapid drying, the materials rapidly revert back to their high molecular weight counterparts. Upon drying, Group 1 Materials are formulated into costly non-aqueous compositions which require expensive carriers (e.g. cyclomethicone) in order to maintain the characteristic of increased sweat inhibition.
TABLE 1Peak 3 +Peak 4 toPeak 4 +SamplePeak 5Peak 42 + 1Peak 3Peak 5ExampleDescriptionBasicityAreaAreaAreaRatioArea1Non-enhanced83%16% 9%74%0.1326%FIG. 1AMaterial2Group 1 Material83% 8%75%17%4.3983%FIG. 1B3Group 2 Material66%72%15%14%1.187%FIG. 4
Group 2 Materials provide increased sweat inhibition and have the added benefit of being stable in aqueous solution for extended periods. (See U.S. Pat. No. 6,902,724 (Parekh), U.S. Pat. No. 6,649,152 (Carrillo) and U.S. Pat. No. 6,991,780 (Carrillo) and references contained therein.) The stability attribute provides for cost savings in manufacturing antiperspirants by eliminating the need for rapid drying, and or permitting the substitution of water for expensive carriers.
The procedure for manufacturing Group 2 Materials requires preparation of high basicity PAC from aluminum metal. Again expensive aluminum powder is recommended for this purpose. High basicity PAC is then enhanced by heating a dilute solution to about 100° C. for several hours. Zirconium components are added either prior to or after the heating process. U.S. Pat. No. 6,649,152 teaches that the aluminum-zirconium salt with high Peak 5 content is preferably spray dried in order to obtain a salt with maximum efficacy. Thus, the procedures for manufacturing Group 2 Materials offer little improvement over the processes for manufacturing Group 1 Materials.
Group 2 Materials are stable over time due to their high Peak 5 composition. Table 1 Example 3 shows the composition of a Group 2 material composed of aluminum and zirconium. The amount of Peak 5 material required to impart stability in aqueous solution is dependent on several factors. In the case of aluminum antiperspirant salts, U.S. Pat. No. 6,902,724 teaches that this stability is imparted when Peak 5 ranges from 15% to 50% and the Peak 4 plus Peak 5 composition is at least 45% and no more than 70%. The report further teaches that the Peak 4 to Peak 3 ratio is unimportant. Although low molecular weight Peak 4 and Peak 5 components are known to provide increased sweat inhibition by blocking pores more effectively than their high molecular weight counterparts, this report teaches away from compositions containing more than 50% Peak 5 and more than 70% Peak 4 plus Peak 5. No examples or explanation is offered with regard to this omission in the teachings.
In the case of aluminum-zirconium antiperspirant salts, U.S. Pat. No. 6,649,152 teaches that stability is imparted when the Peak 5 composition is at least 45%, the Peak 4 to Peak 3 content is typically 20% to about 50%, the Peak 4 to Peak 3 ratio is at least 0.4 and substantially all of the aluminum is found in Peaks 3, 4 and 5. (This set of criteria can be shown to be mathematically equivalent to the criteria shown in Table 2 for Group 2 Materials comprised of aluminum and zirconium.) An aluminum-zirconium antiperspirant salt meeting the requirements of Group 2 Materials is shown in Example 3 of Table 1. In this example the material contains 72% Peak 5, an estimated Peak 4 plus Peak 5 content of 87% and a Peak 4 to Peak 3 ratio of 1.1. The HPLC of this Group 2 Material is shown in FIG. 4. Thus, U.S. Pat. No. 6,649,152 and a related U.S. Pat. No. 6,991,780 which are directed toward Group 2 Material comprised of aluminum-zirconium combinations, teach the benefit of high Peak 5 content with a Peak 4 to Peak 3 ratio of at least 0.4, however their teachings do not address Group 2 Materials of aluminum and zirconium exclusively composed of Peak 5.
Criteria for defining Group 1 Materials and Group 2 Materials based on generally recognized definitions by skilled artisans are summarized below in Table 2.
TABLE 2Al AntiperspirantAl—Zr AntiperspirantCompositionsCompositionsGroup 1Peak 4:Peak3 Ratio >0.5Peak 4:Peak3 Ratio >0.5Materials:Group 2Peak 5 of 15% to 50%Peak 5 >45%Materials:Peak 4:Peak3 Ratio unimportantPeak 4:Peak3 Ratio >0.4Peak 4 + Peak 5 of 45%–70%Peak 4 + Peak 5 >60%
In summary, the efficacy of aluminum and aluminum-zirconium antiperspirants is determined by the amount of low molecular weight Peak 4 and Peak 5 components present. Superior efficacy is obtained when the high molecular weight materials in Peaks 1, 2 and 3 are minimized. When this goal is accomplished by maximizing Peak 4, enhanced efficacy is obtained but the material is unstable in aqueous solution. When this goal is accomplished by maximizing Peak 5, enhanced efficacy and stability in aqueous solution is obtained.
A need therefore exists that overcomes one or more of the above identified issues.